class Base<T extends Base2>{
  T? data;

  Base({this.data});

  factory Base.fromJson(Map<String, dynamic> json) => Base(
    data: json["data"]
    // welcome: json["老师微信"],
    // purple: json["错误信息"],
  );
  aa(){
    data?.fromJson(Map<String,dynamic>());
  }
}

abstract class Base2{
  fromJson(Map<String, dynamic> json);
}